It is well known that silicone rubber is generally inert and is, therefore, particularly well suited for use in medical and scientific fields. For example, silicone rubber is often employed as part of a closure for bottles or containers intended to receive medical or scientific samples. Particularly useful in medical and scientific field is a container utilizing an open top cap, which is a cap with an aperture therein which is in turn sealed by a septum. Sealing the cap's aperture prevents contamination or loss of the sample yet allows a needle to be inserted through the septum of the cap and into the container in order to insert or withdraw the sample. Due to the generally inert nature of silicone rubber and its resealing properties it would be preferred that the septum be comprised, at least in part, of silicone rubber.
The EPA has published standards under 40 C.F.R. .sctn.136 "Guidelines for Establishing Test Procedures for the Analysis of Pollutants" and 40 C.F.R. .sctn.141 "National Interim Primary Drinking Water Regulations: Control of Trihalomethanes in Drinking Water" which relate to acceptable testing procedures. These EPA standards specify a vial/cap/septum combination as well as detailed cleaning and sampling procedures which are designed to ensure that the sample is not contaminated or lost prior to analysis. These EPA regulations specify an open top cap and a septum comprised of silicone rubber laminated with polytetrafluoroethylene (Teflon), such that the face of the Teflon lamination is exposed to the sample.
Although use of a united cap and liner meeting the EPA specifications would be preferred, the industry has to date largely dealt with these requirements by using a separate septum unattached to the cap. Unfortunately, existing methods of attaching a silicone rubber septum to an open top cap are ill-suited for uses related to sampling of scientific or medical samples.
The conventional method of attaching a liner or septum onto a cap utilizes some type of adhesive, which may come in contact with, and potentially contaminate, the sample. In this regard it should be noted that even minor contamination may make critical analytical analysis of pollutants difficult or untrustworthy, since tests are commonly directed towards the presence of pollutants at the level of ppm (part per million) or even ppb (part per billion). Moreover, the EPA specification of a silicone rubber/Teflon septum presents further problems since many adhesives simply do not work well with silicone rubber. In addition, of those adhesives compatible with silicone rubber, many are thermoplastic adhesives which will not withstand common cleaning methods, such as those specified by the EPA cleaning standards.
Other attempts to solve this problem have included curing of the silicone elastomer and a primer directly upon the surface of a polyolefin sheet. For example, in U.S. Pat. No. 4,499,148 issued to Goodale et al. a thin film of polyolefin is corona discharge treated whereupon the uncured silicone is placed together with a primer therebetween. Pressure is then applied to force the materials together and then heat is applied in order to cure the silicone elastomer, thereby bonding the silicone elastomer to the polyolefin sheet as part of the curing process. Thereafter, circular sections of the polyolefin/silicone elastomer laminate are formed and inserted within a polyolefin cap having an aperture in the top. The polyolefin layer of the polyolefin/silicone elastomer laminate is then welded to the interior of the polyolefin cap by ultrasonic welding.
However, this process taught in Goodale '148, as well as the resulting cap, suffers significant drawbacks. Often open top caps leave only a narrow flange, commonly about 3.8 mm or less, on the inside of the cap. Directing the welding energy onto such a narrow surface makes it difficult to consistently obtain a strong bond between the two polyolefin surfaces. Another drawback arises from the use of a polyolefin/silicone elastomer laminate, as opposed to a silicone elastomer alone. The inelasticity of the polyolefin layer makes penetration with a needle difficult and often causes the needle to bend or break, thereby creating significant health and safety concerns and interfering with the use of automatic sampling equipment. However, simply using a thinner polypropylene film in order to decrease the difficulty experienced with inserting the needle causes an increase in welding problems and is not a viable alternative.
Therefore, there exists a need for a cap having an inert elastomer bonded directly to the interior of the cap without the use of adhesives or thin layers of plastic. There further exists a need for such a cap which is capable of withstanding the cleaning procedures required by standard scientific and medical sampling techniques. There likewise exists a need for a cap which will prevent pockets of trapped fluid or air from forming during sampling and cleaning procedures. Moreover, there exists a need for a cap which when utilized to hold medical or scientific samples will not contaminate such samples, allow leakage of such samples or allow the formation of air bubbles within the container. In addition, there exists a need for a method for forming a durable and water resistant bond between inert elastomers, such as silicone rubber, and other materials commonly used in caps and vials. Furthermore, there likewise exists a need for a method for making a durable cap with a septum bonded thereto having the characteristics discussed above.